The present invention is adapted for use with a conventional drive system in which a driven sprocket and a drive sprocket are connected by a flexible drive element such as a drive chain. In such an arrangement, it is well known that the proper functioning of the drive system and the operating life of the drive chain can be significantly enhanced by maintaining the two drive chain runs between the sprockets in tension such that significant slack does not occur in either run. One means of providing such tension is to resiliently bias the sprockets away from one another. However, a more common and typically more convenient arrangement is to provide a tensioning device that biases one or both drive chain runs inward towards the other run at a point intermediate the sprockets. A number of examples of this latter type of tensioning device are disclosed in the prior art. However, in the great majority of prior tensioning devices, the tensioning device is adapted to operate in a particular driven system, e.g., to operate with a given arrangement of sprockets and drive chain.
One result of the fact that prior tensioning devices have been adapted for specific applications is that in essentially all cases, prior tensioning devices have been mounted or secured to a support that is fixed with respect to the sprocket axles. Through use of such a support arrangement, the position of the tensioning device between the sprockets can be controlled, to maintain the tensioning device at the optimum position. The use of fixed supports has been viewed as especially important for tensioning devices adapted to operate with sprockets that are or may be horizontally positioned with respect to one another. In such a horizontal arrangement, the weight of the tensioning device does not affect its position, i.e., the position of the tensioning device between the sprockets is not in any way controlled by gravity acting on the tensioning device.
A further feature of essentially all prior art tensioning devices is that in such devices, the surfaces contacting the two runs of drive chain and urging them inward have either been fixed in position with respect to one another, or resiliently biased towards one another by springs or similar means. A disadvantage of the resilient biasing technique is that it adds complexity to the tensioning device, and the resilient means are themselves subject to wear over time. Tensioning devices having fixed distances between their contact surfaces cannot be adjusted as the chain experiences increased wear. Thus, the tensioning force provided by the device decreases over time, at least in those arrangements where the sprockets are horizontally positioned with respect to one another. A further disadvantage of a fixed distance between contact surfaces is that the tensioning device cannot be used with different sized sprockets.